(1) Field of the Invention
The invention relates to arrays of fibre-optic sensors.
(2) Description of the Art
A fibre-optic sensor package of a known type comprises a package input/output (i/o) fibre and one or more individual fibre-optic sensors, and is arranged to output a finite output pulse series of optical output pulses via the i/o fibre in response to input of one or more interrogating pulses input to the package i/o fibre. Depending on the particular structure of a package, the output pulse series may carry information relating to the temperature, pressure, acceleration etc of the surrounding environment. Such packages typically have an output fibre which allows a portion of one or more interrogating pulses to pass through the package to a second such package which is optically coupled to this portion of fibre, thus providing interrogation of the second package. Many packages may be connected in series to form a line array suitable for gathering information on physical conditions along the line array. In use of the array, one or more interrogating pulses are introduced into an input end of the array and output pulse series from respective packages of the array are output towards the input end of the array.
A problem with such arrays of fibre-optic sensing packages is that in the case of long arrays, having for example several hundred packages arranged in series, the maximum interrogation rate of the array is unacceptably low in certain applications (for example in detection of rapidly changing physical conditions) due to the fact that this rate is fixed by the time taken for a portion of one or more interrogating pulses to reach the last package of the array, and for an output pulse series from the last package to return through every other package to reach the input end of the array.